To all the nay sayers: Kayaks were probably the first hunting boats that were ever made and are still as effective today as they were 4000 years ago. They are safe in cold water as long as you have the proper gear and are comfortable and familiar with you and your kayaks capabilities. Afterall they originated in the Arctic and were used by the Eskimo/Inuit to fish and hunt everything from birds to walrus. All I have is a generic 10' recreation kayak that you can probably get new for less than $300. Its my favorite way to hunt. A friend of mine has a 12' Ascend and its a Cadillac, just real heavy at 80+lbs. I'm sure the 10' is sweet too and lighter
As for gear, there are two schools of thought: 1) you should wear a wetsuit or drysuit and dress to swim, but I don't like to get wet or 2) wear breathable chest waders and a rain jacket and good waterproof gloves (Glacier Glove Ice Bay is my new favorite) and never get wet, but carry a dry bag with a change of clothes, space blanket, a lighter and good fire starters just in case. I take the dry bag with me every time and luckily have never had to use it. The biggest challenge is finding space for everything and to take only what you need. Heavy items (ammo, guns) need to be stowed as low and centered as evenly as possible. Uneven weight distribution can turn a stable kayak into a very tippy one. A decoy bag with backpack straps is the easiest to deal with. Deck rigging is great got the dry bag, lunch cooler, and boat camo. Everyone hunts different and in different places that need different things. It takes some trial and error to figure out what you really need and how to be efficient with it.
As for shooting from the boat... Well, big guns and little boats in cold water make me giddy!! I shoot a 3 1/2" mossberg pump from my boat all the time. Since I'm a righty, I can't shoot very far to the right side of the boat so I try to keep the boat angled so that most of my shots will be over the left side of the boat.
Bottom line, kayaks work. You can do it, but you need to be comfortable in you boat and stay within you and your boats limitations. Make sure to learn those limitations BEFORE duck season and in the warmer months so that your mistakes aren't possibly fatal. Sadly duck hunters are killed every year while in any kind of boat because of weather, accidents and misjudgements. Whatever kind of boat you hunt from, kayak, canoe, jon boat, duck boat, its only as safe as YOU are. What we do is dangerous. The only rule is to never, never, NEVER get wet.